1. Field of the Invention
The present invention relates to an adjusting system and, more particularly, an adjusting system for adjusting a threshold parameter in a wireless receiver in a Code Division Multiple Access (CDMA) communication system. The wireless receiver receives a plurality of external multipath signal. The adjusting system could minimize the probability of acquiring undesired path signals or losing desired path signals.
2. Description of the Prior Art
Spread-spectrum communication systems have been broadly used in the recent years. The Code Division Multiple Access (CDMA) communication technology is adopted in Third Generation Mobile Telephony, and the utilization of the rake receiver is to separate multipath propagated signal components in the CDMA system.
In general, the path signal components must be separated from each other by at least one chip of a spreading code. The rake receiver comprises rake fingers and a delay estimator. Each of these fingers are dispreading and diversity combination, and the delay estimator has a matched filter for each antenna branch and an allocation block for the rake fingers. A signal, received by a spreading code used for signal spreading, of the matched filter is correlated by different delays. The timing of the spreading code then is changed in steps of one chip. When the correlation is high, a multipath propagated signal component can be found and received at the delay found.
The signal will include not only the desired signal but also noise and interference caused by other users or systems. In systems utilizing diversity, the interference of noise can be decreased by a Maximal Ratio Combining (MRC) method. Signals of this method were received via separate antennas weighted in proportion to the signal power of the separate antenna branches. However, this method presumes that the interference of each antenna is independent. This presumption is not always true in actual cellular radio networks, but it is conceivable that the same interference is present at each antenna.
The key point is that the larger ratio of desired signal to noise the less errors will be made. Two important issues are necessary: one is the correction of the timing of the spreading code corresponding to the multipath signal, and the other is that the data of the power ratio and phase corresponding to the multipath signal must be clear. The maximum ratio combiner combines the power ratio and phase of path signal obtained from the tracking unit.
The threshold parameter is a very important criterion when the searcher acquires the multipath signal. The system receives the effective path signal when the power ratio of the path signal is higher than the predetermined threshold parameter. Other path signals are regarded as noises. Consequently, the probability of acquiring undesired path signal or losing desired path signal is highly related to the determining of threshold parameter. Accordingly, it is desirable to determine a proper value of the threshold parameter for receiving the desired path signal, and decreasing the probability of acquiring undesired path signal or losing desired path signal.